To use Joomla site send email, please follow the instructions below to set SMTP authentication in it.
1. Login to your Joomla site as administrator -->Global Configuration-->Server
2. Fill your email account SMTP settings as below
Note: the 'From email' must be same as the 'SMTP Username'.
3. Click Users to modify the Super User email account to the same email address as smtp user above
That's it, you're done.